Rice University researchers use spectral triangulation to pinpoint location of tumors
Bathing a patient in LED light may someday offer a new way to locate tumors, according to Rice University researchers.
A new Rice University method for medical imaging uses strong light from an LED array and an avalanche photodiode detector to pinpoint the location of tumors that have been tagged by antibody-targeted carbon nanotubes. The method can detect fluorescence from single-walled carbon nanotubes (SWCNTs) through up to 20 millimeters of tissue.
Credit: Weisman Lab/Rice University
The spectral triangulation system developed by Rice chemist Bruce Weisman and his colleagues is intended to pinpoint targeted cancer tumors tagged with antibody-linked carbon nanotubes. It is described in a paper in the Royal Society of Chemistry journal Nanoscale.
Because the absorption of short-wave infrared light in tissues varies with its wavelength, spectral analysis of light coming through the skin can reveal the depth of tissue through which that light has passed. This allows the three-dimensional coordinates of the nanotube beacon to be deduced from a small set of noninvasive optical measurements.
The Rice technique relies on the fact that single-walled carbon nanotubes naturally fluoresce at short-wave infrared wavelengths when excited by visible light. A highly sensitive detector called an InGaAs (indium gallium arsenide) avalanche photodiode made it possible to read faint signals from nanotubes up to 20 millimeters deep in the simulated tissue used for lab tests.
"We're using an unusually sensitive detector that hasn't been applied to this sort of work before," said Weisman, a recognized pioneer for his discovery and interpretation of near-infrared fluorescence from single-walled nanotubes.
"This avalanche photodiode can count photons in the short-wave infrared, which is a challenging spectral range for light sensors. The main goal is to see how well we can detect and localize emission from very small concentrations of nanotubes inside biological tissues. This has potential applications in medical diagnosis."
Using light-emitting diodes to excite the nanotubes is effective -- and inexpensive, Weisman said. "It's relatively unconventional to use LEDs," he said. "Instead, lasers are commonly used for excitation, but laser beams can't be focused inside tissues because of scattering. We bathe the surface of the specimen in unfocused LED light, which diffuses through the tissues and excites nanotubes inside."
A small optical probe mounted on the frame of a 3-D printer follows a computer-programmed pattern as the probe gently touches the skin to make readings at grid points spaced a few millimeters apart.
Before reaching the detector, light from the nanotubes is partly absorbed by water as it travels through tissues. Weisman and his team use that to their advantage. "A two-dimensional search tells us the emitter's X and Y coordinates but not Z -- the depth," he said. "That's a very difficult thing to deduce from a surface scan."
Spectral triangulation overcomes the limitation. "We make use of the fact that different wavelengths of nanotube emission are absorbed differently going through tissue," Weisman said. "Water (in the surrounding tissue) absorbs the longer wavelengths coming from nanotubes much more strongly than it does the shorter wavelengths.
"If we're detecting nanotubes close to the surface, the long and the short wavelength emissions are relatively similar in intensity. We say the spectrum is unperturbed.
"But if the emission source is deeper, water in that tissue absorbs the longer wavelengths preferentially to the shorter wavelengths," he said. "So the balance between the intensities of the short and long wavelengths is a yardstick to measure how deep the source is. That's how we get the Z coordinate."
The detector is now being tested in the lab of Dr. Robert Bast, an expert in ovarian cancer and vice president for translational research at the University of Texas MD Anderson Cancer Center.
"It gives us a fighting chance to see nanotubes deeper inside tissues because so little of the light that nanotubes emit finds its way to the surface," Weisman said. "We've been able to detect deeper into the tissues than I think anyone else has reported."
Rice graduate student Ching-Wei Lin is lead author of the paper. Rice research scientist Sergei Bachilo, postdoctoral fellow Michael Vu and Kathleen Beckingham, a professor of biochemistry and cell biology, are co-authors.
The National Science Foundation, the Welch Foundation, the National Institutes of Health and the John S. Dunn Foundation Collaborative Research Award Program supported the research.
Read the abstract at http://pubs.
This news release can be found online at http://news.
Follow Rice News and Media Relations via Twitter @RiceUNews
Bruce Weisman: https:/
Wiess School of Natural Sciences: http://natsci.
Located on a 300-acre forested campus in Houston, Rice University is consistently ranked among the nation's top 20 universities by U.S. News & World Report. Rice has highly respected schools of Architecture, Business, Continuing Studies, Engineering, Humanities, Music, Natural Sciences and Social Sciences and is home to the Baker Institute for Public Policy. With 3,910 undergraduates and 2,809 graduate students, Rice's undergraduate student-to-faculty ratio is 6-to-1. Its residential college system builds close-knit communities and lifelong friendships, just one reason why Rice is ranked No. 1 for best quality of life and for lots of race/class interaction by the Princeton Review. Rice is also rated as a best value among private universities by Kiplinger's Personal Finance. To read "What they're saying about Rice," go to http://tinyurl.
David Ruth | EurekAlert!
Unique brain 'fingerprint' can predict drug effectiveness
11.07.2018 | McGill University
Direct conversion of non-neuronal cells into nerve cells
03.07.2018 | Universitätsmedizin der Johannes Gutenberg-Universität Mainz
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
16.07.2018 | Life Sciences
16.07.2018 | Earth Sciences
16.07.2018 | Physics and Astronomy